In the field of telephony and, in particular, in the field of voice processing telephony, it is often desirable to automatically determine whether a telephone call has been disconnected, i.e., whether a party on the other end of a line has hung up. If a connection was made, for example, through a T-1 digital trunk interface, then each party to the call is notified if the other party has disconnected by changes in well known signaling bits which are periodically transmitted across the telephone network. However, if the call was made through standard analog switches then there is no guarantee that the telephone system will supply any positive signal to indicate that the other party has hung up.
Currently, there are only a few methods which are used to detect disconnection of a call. The first of these methods entails detection of continuous inbound silence since the other party no longer responds. This is not a reliable method since the other party may simply be listening passively, for example, to record messages. Therefore, silence is not a good indication of disconnection. The second of these methods entails detection of inbound dial tone supplied by a central office detector. This is not a reliable method since many central offices fail to supply subscribers any of the signals relied upon for detection. The third and fourth of these methods entail detection of a drop in central office supplied loop current and detection of busy tone, respectively. However, these third and fourth methods suffer from the same disability identified above with respect to the second method.
Thus, there is need in the an for method and apparatus for detecting a disconnect event, i.e., whether a telephone call has been disconnected.